The present invention relates to a seat belt retractor with a web sensor.
A vehicle safety restraint traditionally comprises a seat belt in a so-called three-point configuration. The seat belt comprises a strong woven belt webbing material attached to the vehicle so that it passes horizontally over the lap of a vehicle occupant and diagonally across the vehicle occupant""s torso. Usually one end of the belt webbing is fixed to a structural member such as the floor of the vehicle, typically between a seat and a side of the vehicle. The seat belt then passes across the lap of a vehicle occupant and is releasably fastened to a buckle mounted to a structural member of the vehicle on the other side of the seat. Subsequently the seat belt passes diagonally across the torso of the vehicle occupant and through the loop of a ring attached to a side pillar at approximately the shoulder height of the vehicle occupant. The seat belt then passes vertically downwards and the other end of the seat belt is attached to a seat belt retractor that is bolted to a structural member of the vehicle, such as the floor.
The belt webbing is wound on a cylindrical spool of the seat belt retractor which is spring biased to keep the belt webbing wound onto the seat belt retractor and thus to keep the seat belt secure about the vehicle occupant""s body. Under normal conditions the spool is free to rotate to pay out belt webbing to provide comfort to the vehicle occupant by allowing movement within certain limits, for example to adjust a car radio or access a storage compartment.
However when a crash occurs, the spool must be locked against further payout of belt webbing to prevent the vehicle occupant moving forward and sustaining injury such as by colliding with the dashboard or front windscreen. Traditionally, this is achieved by providing sensors to detect accelerations or decelerations over predetermined limits. A so-called vehicle sensor detects rapid acceleration or deceleration of the vehicle indicative of a crash. A so-called web sensor detects a sudden pull on the belt webbing indicative of a crash.
A web sensor comprises an eccentrically pivoted inertia member mounted to the spool to rotate with the spool under normal conditions, but biased by a calibration spring. When the spool moves suddenly, indicating a crash, the inertia member lags behind the spool and effectively pivots relative to the spool. The inertia member incorporates an integral locking pawl that engages with teeth on a ratchet wheel, known as a lock cup, attached to the locking system. This locks the spool against further payout of belt webbing and thus secures the vehicle occupant.
However, the integral pawl is at a relatively long distance from the pivot point of the disc and is thus at a particularly acute angle to the load vector. It has been found that this arrangement increases the possibility of the seat belt retractor jamming due to the pawl and the lock cup teeth hitting each other tip to top. Jamming is decreased if a separate locking pawl is used but this increases the cost of the seat belt retractor.
The present invention aims to eliminate the tendency to jam in a cost effective manner.
According to the present invention there is provided an improved arrangement and shape for the locking pawl and of the teeth of the lock cup.